case. >> at this early stage, they have moved so quickly. you and i spoke yesterday. they're going to crunch through a lot of data, a lot of video. how are they able to identify a suspect so quickly either from the cell phone video or from that department store video? >> well, one of the things they have to do is find the location where those explosions took place. obviously, they can do that on film. then they have to back up from that and see if there's any indication whatsoever that a device, a backpack, something had been laid down, when they see that, they keep backing up until they find the source of that. so, really, they're going over about an hour and a half of film during that critical period of time. they know when the blast went off. now, they have to find out who set that package down that caused it. >> again, and that picture of an individual, about 6 feet tall, wearing a white or off-white baseball cap, cliff van zant getting down to the detail.